The Integumentary System BIOL2012SEF PDF

The Integumentary System BIOL2012SEF Dr Emily Wong 1 2 Epidermis        The outermost layer of skin (the skin that we see) Compose of 4-5 layers of epithelial cells Contains 4 principal types of cells Avascular (without blood vessels) Impermeable to water (water-repellent) Physically tough Re...

The Integumentary System BIOL2012SEF Dr Emily Wong 1 2 Epidermis        The outermost layer of skin (the skin that we see) Compose of 4-5 layers of epithelial cells Contains 4 principal types of cells Avascular (without blood vessels) Impermeable to water (water-repellent) Physically tough Relatively dry at the surface to impede the growth of microorganisms 3 Epidermis  Divided into   5 layers (in finger tips, palms & soles) 4 layers (without stratum lucidum in most regions) 4 5 Epidermis  The outer surface of epidermis (the part you can touch), is made up of dead skin cells     The dead cells are constantly being shed, at a rate of ~30000-40000 each minute e.g when you go swimming for a long time, the dead cells on your skin’s surface absorb water and swell, causing the skin to wrinkle The skin does not get thinner as the dead cells are shed, because they are continuously replaced from below e.g In the human forearm, about 1300 cells/cm2/hr are shed and commonly accumulate as house dust. 6 Epidermis  4 principal types of cells     Keratinocytes Langerhans cells Merkel cells Melanocytes 7 Epidermis     It contains squamous cells or keratinocytes, which synthesize a tough insoluble protein called keratin. About 90% of epidermal cells are keratinocytes. Keratin is a major component of skin, hair and nails. Keratinocytes on the surface of the epidermis are dead and are continually shed and replaced by cells from beneath. 8 Epidermis      This layer also contains specialized cells called Langerhans cells that signal the immune system of an infection. The innermost layer of the epidermis (stratum basale) contains keratinocytes called basal cells. These cells constantly divide to produce new cells that are pushed upward to the layers above. Basal cells become new keratinocytes which replace the older ones that die and are shed. Also found in the basal layer of the skin are touch receptor cells called Merkel cells. 9   Within the basal layer are melanin producing cells known as melanocytes. Melanin is a pigment that helps to protect the skin from harmful ultraviolet solar radiation by giving it a brown hue. 10 11 Melanocytes Do some people have more melanocytes than other people? 12 Epidermis       The deepest layer of epidermis contains rapidly dividing cells As new cells are produced, older cells are pushed toward the surface They flatten and die because they no longer receive nourishment from the dermis ~2 weeks to a month pass from the time a new cells is formed to the time it is shed When the epidermis is injured or diseased, its replacement speeds up in response A tough and fibrous protein, keratin, gradually replaces the cytoplasmic content of the cells 13 Stratum basale   Sometimes called “stratum germinativum” Contains germinal cells      Cells are produced from the stratum basale by mitosis and these move outwards (exterior), undergoing a process known as keratinization Finally to be shed from the surface as fully keratinized dead squamous cells Takes 2-4 weeks to pass from stratum basale to the surface Undergoes a number of transitions Other cells:   Melanocytes: responsible for skin pigmentation Langerhans cell (specialized dendritic cell), similar to Macrophages 14 Langerhans cell (Dendritic cell) 15 Section of skin showing large numbers of dendritic (Langerhans) cells in the epidermis 16 Langerhans cell    Are “guard” cells that constantly patrol the epidermis Look like “spiders”- has many tentacle-like structures called dendrites Sensitive to sun exposure    Knock the cells out of commission When the cells are “on sick leave”, the skin is vulnerable to other microorganisms Explain why people get flares of herpes simplex (fever blisters) when they are exposed to the sun 17 Stratum spinosum     Lies immediately over the basal layer Consist 2-6 rows of polyhedral cells (spinous cells) Become more flattened as they move towards the surface Cells appeared to be joined together by intracellular bridges (desmosomes) giving cells a spiny appearance 18 Stratum granulosum    Above the spiny cells found between the stratum corneum (and possibly stratum lucidum) and stratum spinosum Consists of 1-3 layers diamond-shaped cells    keratinocytes are now called granular cells These cells have have darkly-staining nuclei Packed with basophilic granules (keratohyaline granules) 19 Stratum lucidum     Above the granular layer Found only in thick skin (the thicker skin of the palms and soles) Composed of three to five layers of dead, flattened keratinocytes Contain droplets of an oily substance (produced as a result of the disintegration of the lysosomes) 20 Stratum corneum     Outermost layer of the epidermis Varies in thickness depending on the region of the body Composed of large, flat, polyhedral, plate-like envelopes filled with keratin, which is made up of dead cells that have migrated up from the stratum granulosum Subject to pressure, the layer of keratinized cells is dense and compact   flat, anucleate, cornified dead cells 21  Rich in keratin    renders the skin tough, pliable and relatively impermeable to substances passing in or out of the body that helps keep the skin hydrated by preventing water evaporation The transformation of cells into “keratinocytes” is referred to as keratinization  this term encompasses the transition undergone by a living epidermal cell as it moves outwards to the exterior eventually forming a flattened dead cells of the stratum corneum 22 23 Dermis      Just beneath the epidermis and consist primarily of fibres (collagen and elastin) and ground substance (polysaccharide) This is the thickest layer of skin composing almost 90% of its thickness. Much thicker than epidermis (~2mm) Mostly 0.8mm 5mm in sole and palm 24 Dermis   Contains blood vessels, hair follicles, oil glands, sweat glands, sensory structures, and nerve endings Unlike epidermis, dermis does not wear away  e.g tattoo-droplets of ink are injected into the dermal layer 25 Dermis   Subdivided into the papillary and reticular layers Papillary dermis:       Superficial part of dermis Contains glycosaminoglycans (GAGs) – important in regulating the appearance of skin surface a type of complex carbohydrate Moisture- attracting property: attracted to water (capable of binding up to 1000 times their weight in water) Decrease in number of GAGs with age Reticular dermis:  Within the reticular dermis are structures called rete pegs 26 rete pegs (epidermal ridges)    These pegs extend up into the epidermis and are responsible for holding the epidermis and dermis together Increase frictions and surface area of epidermis Forming fingerprints ∵ epidermal ridge pattern is genetically determined, this gives rise to uniqueness of individual 27 28 Ridges help the epidermis bind to the dermis. The uneven ridges create fingerprints!! 29 30 Components of the dermis include:    Blood vessels: transport oxygen and nutrients to the skin and remove waste products. These vessels also transport vitamin D from the skin to the body. Lymphatic ducts: supply lymph (milky fluid containing white blood cells of the immune system) to skin tissue to fight microbes. Sweat glands: regulate body temperature by transporting water to the skin's surface where it can evaporate to cool down the skin. 31 Components of the dermis include:    Sebaceous gland (Oil gland): secrete sebum to lubricate the skin and hair Hair follicles: tube-shaped cavities that enclose the hair root and provide nourishment to the hair. Sensory receptors: nerve endings that transmit sensations such as touch, pain, and heat intensity to the brain. 32 33 Sweat glands   Produce sweat (water, salts, lactic acid, vitamin C, and metabolic wastes) Found over the whole surface of skin    Functions:    2-5 millions in human abundant on the palms and soles eliminate wastes regulate body temperature by evaporating from the skin surface Wax gland: modified sweat glands   found in the external ear canal Produce wax – protects the ear by trapping small particles 34 Sebaceous gland (Oil gland)    are microscopic glands in the skin secrete an oily matter (sebum) in the hair follicles to lubricate the skin and hair found virtually all over the body  ~ 400-900 glands per cm2 on forehead and scalp  ~